Tumor necrosis factor (TNF) is a pleiotropic cytokine, produced by a number of cell types, mainly by activated macrophages. It is one of the principal mediators of the immune and inflammatory response. Interest in its function has greatly increased, recently, in view of evidence of the involvement of TNF in the pathogenesis of a wide range of disease states, including endotoxin shock, cerebral malaria and graft-versus-host reaction. Since many of the effects of TNF are deleterious to the organism, it is of great interest to find ways of blocking its action on host cells. An evident target for such intervention are the molecules to which TNF has to bind in order to exert its effects, namely the TNF-Rs. These molecules exist not only in cell-bound, but also in soluble forms, consisting of the cleaved extra-cellular domains of the intact receptors (see Nophar et al., EMBO Journal, 9(10):3269-78, 1990). The soluble receptors maintain the ability to bind TNF, and thus have the ability to block its function by competition with surface receptors.
Another method of TNF inhibition based on the principle of competing with cell-bound molecules, is the use of antibodies recognizing TNF receptors and blocking the ligand binding.
The cell surface TNF-Rs are expressed in almost all cells of the body. The various effects of TNF, the cytotoxic, growth-promoting and others, are all signalled by the TNF receptors upon the binding of TNF to them. Two forms of these receptors, which differ in molecular size: 55 and 75 kilodaltons, have been described, and well be called herein p55 and p75 TNF-R, respectively. It should be noted, however, that there exist publications which refer to these receptors also as p60 and p80.
The TNF-Rs belong to a family of receptors which are involved in other critical biological processes. Examples of these receptors are the low affinity NGF receptor, which plays an important role in the regulation of growth and differentiation of nerve cells. Several other receptors are involved in the regulation of lymphocyte growth, such as CDw40 and some others. Another member of the family is the FAS receptor also called APO, a receptor which is involved in signalling for apoptosis and which, based on a study with mice deficient in its function, seems to play an important role in the etiology of a lupus-like disease. Herein, this family of receptors is called "TNF/NGF receptor family".
One of the most striking features of TNF compared to other cytokines, thought to contribute to the pathogenesis of several diseases, is its ability to elicit cell death. The cell-killing activity of TNF is thought to be induced by the p55 receptor. However, this p55 receptor activity can be assisted by the p75 receptor, through a yet unknown mechanism.
Parent application number 07/524,263 and European patent publication nos. 0,398,327 and 0,412,486 disclose antibodies to the soluble TNF-Rs. These antibodies were found to recognize the soluble TNF-Rs and to inhibit the binding of TNF to the TNF-Rs on the cell surface. Monovalent F(ab) fragments blocked the effect of TNF, while intact antibodies were observed to mimic the cytotoxic effect of TNF.